A typical multi-color dye donor web that is used in a thermal printer is substantially thin and has a repeating series of three different rectangular-shaped color sections or patches such as a yellow color section, a magenta color section and a cyan color section. Also, there may be a transparent colorless laminating section immediately after the cyan color section.
Each color section of the dye donor web consists of a dye transfer area that is used for dye transfer printing and a pair of opposite longitudinal edge areas alongside the dye transfer area which are not used for printing. The dye transfer area is about 95% of the web width and the two edge areas are each about 2.5% of the web width.
To make a multi-color image print using a thermal printer, a motorized donor take-up spool pulls the dye donor web from a donor supply spool in order to successively advance an unused single series of yellow, magenta and cyan color sections over a stationary bead of selectively heated resistive elements on a print head between the two spools. Respective color dyes within the yellow, magenta and cyan color sections are successively heat-transferred via the bead of selectively heated resistive elements, in superimposed relation, onto a dye receiver such as a paper or transparency sheet or roll, to form the color image print. The bead of resistive elements extends across the entire width of a color section, i.e. across its dye transfer area and its two edge areas alongside the transfer area. However, only those resistive elements that contact the dye transfer area are selectively heated. Those resistive elements that contact the two edge areas are not heated. In other words, the dye transfer is effected from the transfer area to the receiver medium, but not from the two edge areas to the receiver medium.
As each color section, including its dye transfer area and its two edge areas, is advanced over the bead of selectively heated resistive elements, the color section is subjected to a longitudinal tension particularly by the pulling force of the donor take-up spool. Since the dye transfer area is heated by the resistive elements, but the two edge areas alongside the transfer area are not, the transfer area is significantly weakened in relation to the edge areas. Consequently, the longitudinal tension will stretch the dye transfer area relative to the two edge areas. This stretching causes the dye transfer area to become thinner than the non-stretched edge areas, which in turn causes creases or wrinkles to develop in the transfer area, particularly in those regions of the transfer area that are close to the edge areas. The longitudinal creases or wrinkles are most notable in the regions of the dye transfer area that are close to the two edge areas because of the sharp, i.e. abrupt, transition between the weakened transfer area and the stronger edge areas.
As the donor web is advanced, the creases or wrinkles tend to spread or extend from a trailing or rear end portion of a used dye transfer area at least to a leading or front end portion of the next dye transfer area to be used. A problem that can result is that a crease or wrinkle in the leading or front end portion of the next dye transfer area to be used will cause an undesirable line artifact to be printed on a leading or front end portion of the dye receiver when dye transfer occurs at the crease. The line artifact printed on the dye receiver is relatively short, but quite visible.
The question presented therefore is how to solve the problem of the creases or wrinkles being created in an unused transfer area so that no line artifacts are printed on the dye receiver.
The Cross-Referenced Application
The cross-referenced application discloses a method of equalizing web-stretching caused by web tensioning in a dye transfer printer that is for use with a donor web having a dye transfer area and opposite longitudinal edge areas alongside the transfer area. The method includes the steps of heating a dye transfer area to effect a dye transfer from the transfer area to a dye receiver, and uniformly heating the two edge areas alongside the transfer area less than the transfer area is heated, but sufficiently so that the edge areas may be stretched by tension substantially the same as the transfer area may be stretched. If the two edge areas alongside a dye transfer area being used in the printer are stretched substantially the same as the dye transfer area, the likelihood of any creases or wrinkles being created in the next unused transfer area is substantially reduced. Thus, no line artifacts will be printed on a dye receiver in the printer.